From European Patent Specification No. 263,566 a field of artificial grass is known which is in particular intended for soccer, whereby measures have been taken to make those fields of artificial grass, which so far have been used for playing hockey thereon, suitable for playing soccer thereon as well. These measures consist of frizzing the fibrous material and applying a substance on said fibrous material, as a result of which the coefficient of friction of the fibrous material is reduced. The field of artificial grass such as described in European Patent Specification 263.566 constitutes a considerable improvement compared to the known fields of artificial grass known at that time, but thanks to further developments it has been found possible to develop a field of artificial grass which more adequately satisfies the demands to be made of fields of artificial grass, in order to be able to practice a certain sport, such as soccer, thereon.
European Patent Specification No. 260,769 teaches that the substructure is important for a field of artificial grass, in particular for those sports whereby jumps are made on the field of artificial grass. So far the influence of such a substructure has been greater with fields of artificial grass on which soccer was played than with fields of artificial grass on which hockey was played. The field of artificial grass according to the invention proposed herein is less dependent on the substructure, at least less dependent on the specific measures such as described in European Patent Specification No. 260,769.
From European Patent Application No. 174,755 a method is known for providing a field containing artificial grass on a footway or on a sports field, by laying a layer with an open structure provided with artificial grass fibres and providing a particulate material, such as sand or ground particles, between said fibres. If such a mat is laid on ground in which natural grass can be made to grow, by providing natural grass seeds in said mat, the grass can be made to grow through the mat in which the artificial grass is incorporated. Thus a combination of artificial grass and natural grass is obtained.
From German Offenlegungsschrift No. 2,522,864 a method is known for protecting plants and the like, such as also natural grass on so-called grid stones, by providing artificial grass fibres around said grid stones or structural elements. Such grid stones are unsuitable for laying fields of artificial grass, however.
A field containing artificial grass comparable with the construction such as described in European Patent Application No. 174,755 is also mentioned in European Patent Application No. 403,008 (published on Dec. 19, 1990), which describes a sports field on a mat of artificial grass, rooted through with roots of grass plants penetrating the mat of artificial grass. Tests which have been taken, however, show that the growth of the natural grass is strongly impeded by the mat in which the artificial grass is provided, in spite of the fact that openings are provided all over the surface of the mat of artificial grass, as a result of which the grass plants grow from the foundation (see column 1, lines 46-49 of said European Patent Application No. 403.008).